The present invention relates to a core bar for steering wheels.
Typically, the core bar for steering wheels is formed, for example, by bending and welding an iron bar, or by integral casting of a magnesium alloy material, etc. However, the use of an iron material increases a mass of the core bar and makes weight reduction difficult. On the other hand, the use of a lightweight alloy material such as magnesium alloy enables a reduction in weight, but increases the difficulty of reducing manufacturing costs due to expensive material and the need for finish machining.
In light of these problems, JP-A 57-158158 and JP-A 60-60065 propose two half members each produced by press forming steel plate which are butt-welded to form a hollow core bar. The structure having butt-welded half members allows a reduction both in mass, due to use of a relatively thin steel plate, and in complexity of finish machining due to the use of press forming.
Moreover, a steering wheel is arranged at a given angle and opposite to a driver or an occupant, so that part of a rim or a ring grip of the steering wheel is located relatively close to a driver""s abdomen during operation. In consideration of possible collision between the driver and the steering wheel at collision of a vehicle, the rim, etc. are formed to deform and to alleviate any impact of the steering wheel on the driver.
In terms of the impact absorbing characteristics, it is desirable that deformation of the steering wheel occurs so that the rim becomes parallel to the driver without significant change in overall shape of the steering wheel.
However, with the hollow core bar produced by butt-welding half members of a press-formed steel plate, the hollow core bar is apt to strongly resist deformation before being crushed, and to undergo significant change in shape due to total crush when subjected to a force in excess of a predetermined limit. Thus, the realization of desired impact absorbing characteristics for the core bar requires adoption of a complicated shape and/or special materials, thus inducing the drawback of increased manufacturing cost.
It is, therefore, an object of the present invention is to provide a core bar for steering wheels which exhibits excellent impact absorbing characteristics along with reduced weight and manufacturing cost.
The present invention generally provides a core bar for a steering wheel mounted to a steering shaft, comprising: a first half shell; and a second half shell coupled to the first half shell, each half shell comprising: a boss portion coupled to the steering shaft, the boss portion including a boss-edge coupling part for coupling the first and second half shells along edges thereof, a shaft fixing part placed substantially in a center of the boss portion and mounted to the steering shaft, and a zone of reduced mechanical strength, xe2x80x9cweak partxe2x80x9d or zone of weakness which is defined between the boss-edge coupling part and the shaft fixing part and wherein the first and second half shells face each other without being coupled; a rim portion including a rim-edge coupling part for coupling the first and second half shells along the edges thereof and a rim hollow part defined between the first and second half shells; and a spoke portion interposed between the boss portion and the rim portion, the spoke portion including a spoke-edge coupling part for coupling the first and second half shells along the edges thereof and a spoke hollow part defined between the first and second half shells.
One aspect of the present invention is to provide a core bar for a steering wheel mounted to a steering shaft, comprising: a first half shell; and a second half shell coupled to the first half shell, each half shell comprising a boss portion, a rim portion and a spoke portion, the rim and spoke portions comprising a flange arranged along one of the edges of the first and second half shells, an embracement arranged along another of the edges for holding the flange, and a hollow defined between the first and second half shells, respectively, the spoke portion comprising, in the vicinity of a connection to the rim portion, a part with greater section than that of an adjacent part.
A further aspect of the present invention is to provide a core bar for a steering wheel mounted to a steering shaft, the steering shaft being provided with a fixation part to which a tightening means is tightened in a predetermined axial direction, an engagement part engaging in a direction of rotation, and a tapered part tapering in an opposite axial direction to the predetermined axial direction, the core bar comprising: a boss portion coupled to the steering shaft, the boss portion including a main body comprising a first reception engaged with the fixation part of the steering shaft and a second reception engaged with the engagement part of the steering shaft, and a block comprising a third reception engaged with the tapered part of the steering shaft and pressed in the opposite axial direction and a support pressing the second reception against the engagement part of the steering shaft; a rim portion; and a spoke portion interposed between the boss portion and the rim portion.